1,1-Difluoroolefins are compounds that have attracted a great deal of attention because of their ability to react with various organic molecules. For example, these compounds have found application in designing diverse biological systems where they function as a mechanism-based enzyme inhibitor. They have been found to exhibit biocidal activity and can be used against pests that affect plants and animals. They have also been found to be a bioisostere of aldehydes and ketones. In addition, difluorovinyl cycloaliphatic compounds have been used as intermediates to difluoromethyl ethers for use as liquid crystal displays and as monomers for fluoroquinodimethane polymers.
The following articles and patents are representative of methods for forming 1,1-difluoroalkenes. They include:
Kyung II Kim, et al, A New Route to 1,1-Difluoroolefins From Carboxylic Acids, Tetrahedron Letters, Vol. 19, 3223–3226 (1996) disclose methods for the synthesis of 1,1-difluoroolefins suitable for the design of biologically active molecules. Disclosed as the most versatile method for producing 1,1-difluoroolefins is the Wittig olefin synthesis. In this process an aldehyde is reacted with a phosphine, e.g., triphenylphosphine and sodium chlorodifluoroacetate. In their new route, carboxylic acids are converted first to dithioesters in a one-pot procedure. Then, HgF2 is reacted with the dithioesters in the presence of HF-pyridine and KF to produce difluorothioethers which are oxidized to the corresponding sulfoxides and heated to produce the 1,1-difluoroolefins.
Matthews, D. P., et al, A New Method For The Electrophilic Fluorination of Vinyl Stannanes, Tetrahedron Letters, Vol. 34, No. 19, pp 3057–3060, 1993 disclose the use of vinyl stannanes for producing terminal fluoroolefins. In this process the fluoro vinyl stannanes substrates are prepared by the Horner-Wittig reaction of protected ketones with diethyl 1-fluoro-1-(phenylsulfonyl)methanephosphanate followed by conversion of the fluorovinyl sulfones to (fluorovinyl) stannanes by reaction with tributyltin hydride in refluxing benzene. Electrophilic fluorination of the vinyl stannanes is effected by reaction with 1-chloromethyl-4-fluoro-1,4-diazoniabicyclo[2.2.2.]octane bis(tetrafluoroborate).
Fuqua, S. A., et. Al, Synthesis of 1,1-Difluoro Olefins. II. Reaction of Ketones With Tributylphosphine and Sodium Chlorodifluoracetate, J. Am. Chem. Soc. 1965, 2543 disclose the formation of 1,1-difluoroolefins by reaction of aldehydes with triphenylphosphine and sodium chlorodifluoroacetate. The same reaction substituting a ketone for the aldehyde was not successful. However, replacement of triphenylphosphine with tributylphosphine and combining with N-methylpyrrolidone gave good yields.
U.S. Pat. No. 4,997,855 discloses the use of vinyl fluorides such as 11-bromo-1,1-difluoro-1,11-dodecadiene, 1,1-difluoro-2-methyl-1-dodecene, 1,1-difluoro-1-tetradecene and 1,1,2-trifluoro-1-dodecene for controlling nematodes and insects. Example 1 shows the preparation of such vinyl fluorides, e.g., the reaction of 1-difluoro-1-tetradecene with tridecylic aldehydes, dibromodifluoromethane and dimethylacetamide. Zinc dust is added to generate a precipitate. On filtering the filtrate is further purified to generate the desired product.
U.S. Pat. Nos. 4,839,390 and 4,968,851 disclose methods for combating arthropods and nematodes by the application of a long-chain halogen olefin. The long chain halogen olefins are obtained by reacting a triphenylphosphonium salt with chlorodifluoromethane in the presence of a C1-4 alkyl-lithium compound.
U.S. Pat. Nos. 6,605,747 and 2002/0120,168 disclose the preparation of 1.1-difluoromethyl substituted cyclohexane ethers for use as liquid crystal compositions via a difluorovinyl intermediate. The difluorovinyl intermediate is formed by the reaction of the corresponding cyclohexanones or aldehydes with CF2Br2 and tributylphosphine.
Legros, J. et al, Trifluoromethylcyclohexane As A New Solvent? Limits Of Use, Tetrahedron 58 (2002) pp 4067–4070) discuss the stability aspects of trifluoromethylcyclohexane as a solvent. In the body of the article the dehydrofluorination of the trifluoromethyl group was attempted without success. Specifically, base dehydrofluorination of trifluoromethylcyclohexane using t-butyl Li in the presence of tetramethylenediamine or using t-BuOK or n-BuLi in Et2O are reported as unsuccessful.